1. Field of the Invention
The present invention relates to an apparatus for switching a visual field frame of a view finder of a camera, an operation apparatus therefor, and an apparatus for actuating a rotary operation member having a neutral position.
2. Description of the Related Art
In a known APS (Advanced Photo System) camera using a self-advancing type of film cartridge, the picture plane size can be switched among a standard picture plane (high-vision size ratio of approximately 9:16), a narrow-width picture plane (classic size ratio of approximately 2:3) in which the lateral width of the standard field of view is reduced by partly interrupting the right and left sides of the standard picture plane, and a laterally-elongated picture plane (panoramic size ratio of approximately 1:3) in which the vertical length of the standard picture plane is reduced by partly interrupting the upper and lower sides of the standard picture plane. In such a camera, upon photographing, an object image is formed on a film at the standard picture plane size and data on the selected picture plane size for each frame of the film is magnetically recorded. The process to imprint the object image into each frame of selected picture plane size is carried out at the development stage or a stage subsequent thereto in accordance with the magnetically recorded data. Therefore, it is not necessary to provide a light intercepting mechanism in a light path of a photographing optical system of the camera in order to vary the lengthwise-crosswise ratio of the picture plane size. However, it is necessary to indicate the selected picture plane size in the finder in order to make it possible for a photographer to determine the composition. To this end, a field frame switching device is provided in the finder optical system.
For example, to realize a mechanical device for switching the (visual) field frame, a pair of L-shaped light-interception members can be provided opposed to form a laterally-elongated rectangular field frame, wherein the L-shaped light-interception members are moved in directions parallel with the major and minor sides of the rectangular field frame to define the narrow-width field of view corresponding to the classic size or the laterally-elongated field of view corresponding to the panoramic size, with respect to the standard field of view corresponding to the high vision size. However, in this arrangement, since the L-shaped light-interception members are moved in orthogonal directions, it is necessary to provide spaces substantially identical in size to the width of the light-interception members in the lengthwise and crosswise directions, so that the latter can be retracted and accommodated in the spaces. Moreover, a drive mechanism and a support mechanism to move and support the light-interception members in the lengthwise and crosswise directions are complicated.
Furthermore, since the finder field frame switching mechanism is complex, the incorporation of the same into the camera is troublesome. In particular, in an APS camera, since three different sizes of picture plane are possible, as mentioned above, the field frame switching mechanism is more complex and hence, it takes more time to assemble the camera than a normal camera.
In addition to the foregoing, in the above-mentioned field frame switching mechanism, if the movable light-interception members are directly connected to an external operation device, when the light-interception members are moved by the external operation device, a mal-function of the light-interception members may occur due to the assembling error. To prevent this, there is a `play` (tolerance) provided between the operation device and the light-interception members. It is preferable in view of the facilitation of the assembling operation that the play be large since camera components become small as the camera becomes compact. However, the play provided between the light-interception members and the operation device causes the following problems:
In an APS camera, since the light-interception members are moved to narrow the width of the picture plane or laterally-elongated the picture plane with respect to the standard picture plane (neutral position), it is necessary to provide a holding means for holding the light-interception members at the neutral position. If the neutral position holding means is provided on the movable light-interception members, the structure is complicated, thus resulting in a deteriorated assembling operation. Therefore, the neutral position holding means is usually located on the operation device. For instance, a dial member which can be externally rotated is provided with a click stop mechanism, so that the light-interception members can define predetermined sizes of the field frame corresponding to a plurality of click positions of the dial member. However, since there is play between the operation device and the light-interception members and there is no mechanism which holds the light-interception members at the neutral position, there is a possibility that the positional deviation of the light-interception members takes place. Moreover, if the neutral position holding means is composed only of an engagement mechanism such as a click stop mechanism, the positional deviation of the light-interception members occurs due to the error in the holding means. Also, an error in the amount of play between the operation device and the light-interception members must be taken into account to precisely move the light-interception members from the neutral position to a predetermined position in the forward or reverse direction.
The above-mentioned problem can be applied not only to the field frame switching mechanism of the finder, but also, for example, to the rotary operation member which has a neutral position and predetermined angular positions on opposite sides of the neutral position in the forward and reverse directions. Namely, if the rotary operation member and the operation device are assembled with a tolerance therebetween, it is difficult to obtain the correct neutral position and the correct angular positions.